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| United States Patent |
5,232,576
|
|
Matsumoto
, et al.
|
August 3, 1993
|
Anode for chromium plating and processes for producing and using the same
Abstract
There are described an anode, a process for producing the same, an
apparatus for electrolytic chromium plating, and a method for electrolytic
chromium plating, using such anode, wherein the anode comprises an
electrically conductive substrate comprising a valve metal or an alloy
thereof, a first intermediate layer formed on the sustrate and comprising
an oxide of tin, a second intermediate layer formed on the first
intermediate layer and comprising either (1) platinum metal and an oxide
of tin, or (2) platinum metal, an oxide of tin, and iridium oxide, and a
surface layer formed on the second intermediate layer and comprising
either (1) platinum metal and an oxide of tin, or (2) platinum metal, an
oxide of tin, and iridium oxide, the composition of said surface layer
being different form that of said second intermediate layer.
| Inventors:
|
Matsumoto; Yukiei (Kanagawa, JP);
Sekimoto; Masao (Kanagawa, JP)
|
| Assignee:
|
Permelec Electrode Ltd. (Kanagawa, JP)
|
| Appl. No.:
|
755423 |
| Filed:
|
September 4, 1991 |
Foreign Application Priority Data
| Current U.S. Class: |
205/284; 204/290.08; 204/290.09; 427/125; 427/126.5 |
| Intern'l Class: |
C25D 017/10; C25D 003/04; B05D 005/12 |
| Field of Search: |
204/290 F,242
205/284
427/126.5,125
|
References Cited
U.S. Patent Documents
| 3882002 | May., 1975 | Cook, Jr. | 204/290.
|
| 4581117 | Apr., 1986 | Asano et al. | 204/290.
|
Other References
Chemical Abstract 95: 51800e, Aug. 10, 1981.
Chemical Abstract 101: 179898c, Nov. 12, 1989.
Chemical Abstract 108: 121032u, Apr. 4, 1988.
Chemical Abstract 111: 242636q, Dec. 25, 1989.
|
Primary Examiner: Niebling; John
Assistant Examiner: Bolam; Brian M.
Attorney, Agent or Firm: Sughrue, Mion, Zinn, Macpeak & Seas
Claims
What is claimed is:
1. An anode for chromium plating which comprises an electrically conductive
substrate comprising a valve metal or an alloy thereof, a first
intermediate layer formed on the substrate and comprising an oxide of tin,
a second intermediate layer formed on the first intermediate layer and
comprising either (1) platinum metal and an oxide of tin, or (2) platinum
metal, an oxide of tin, and iridium oxide, and a surface layer formed on
the second intermediate layer and comprising either (1) platinum metal and
an oxide of tin, or (2) platinum metal, an oxide of tin, and iridium
oxide, the composition of said surface layer being different from that of
said second intermediate layer.
2. An anode as in claim 1, wherein the amount of the tin oxide fixed on the
substrate in said first intermediate layer is from 0.5 g/m.sup.2 to 30
g/m.sup.2.
3. An anode as in claim 1, wherein the amount of the tin oxide fixed on the
substrate in said first intermediate layer is from 0.5 g/m.sup.2 to 10
g/m.sup.2.
4. An anode as in claim 1, wherein in said second intermediate layer, the
proportion of at least either of platinum and iridium oxide to tin oxide
is from 30:70 to 60:40 by mol and the content of iridium oxide is 10 mol %
or less.
5. An anode as in claim 1, wherein in said surface layer, the proportion of
at least either of platinum and iridium oxide to tin oxide is from 70:30
to 90:10 by mol and the content of iridium oxide is 10 mol % or less.
6. A process for producing an anode for chromium plating which comprises
coating a solution containing a tin compound on a substrate comprising a
valve metal or an alloy thereof, heat-treating the coating in an oxidizing
atmosphere to form a first intermediate layer comprising an oxide of tin,
coating the first intermediate layer with a second intermediate
layer-forming coating solution containing either (1) a platinum compound
and a tin compound, or (2) a platinum compound, a tin compound, and an
iridium compound, heat-treating the second intermediate layer coating in
an oxidizing atmosphere to form a second intermediate layer comprising
either (1) platinum metal and an oxide of tin, or (2) platinum metal, an
oxide of tin, and iridium oxide, subsequently coating the second
intermediate layer with a surface layer-forming coating solution
containing either (1) a platinum compound and a tin compound, or (2) a
platinum compound, a tin compound, and an iridium compound, and different
in ingredient composition from the second intermediate layer, and then
heat-treating the surface layer coating in an oxidizing atmosphere to form
a surface layer comprising either (1) platinum metal and an oxide of tin,
or (2) platinum metal, an oxide of tin, and iridium oxide.
7. A method of electrolytic chromium plating which comprises conducting
electrolytic chromium plating using an anode comprising an electrically
conductive substrate comprising a valve metal or an alloy thereof, a first
intermediate layer formed on the substrate and comprising an oxide of tin,
a second intermediate layer formed on the first intermediate layer and
comprising either (1) platinum metal and an oxide of tin, or (2) platinum
metal, an oxide of tin, and iridium oxide, and a surface layer formed on
the second intermediate layer and comprising either (1) platinum metal and
an oxide of tin, or (2) platinum metal, an oxide of tin, and iridium
oxide, the composition of said surface layer being different from that of
said second intermediate layer.
8. An apparatus for electrolytic chromium plating including an anode which
comprises an electrically conductive substrate comprising a valve metal or
an alloy thereof, a first intermediate layer formed on the substrate and
comprising an oxide of tin, a second intermediate layer formed on the
first intermediate layer and comprising either (1) platinum metal and an
oxide of tin, or (2) platinum metal, an oxide of tin, and iridium oxide,
and a surface layer formed on the second intermediate layer and comprising
either (1) platinum metal and an oxide of tin, or (2) platinum metal, an
oxide of tin, and iridium oxide, the composition of said surface layer
being different form that of said second intermediate layer.
Description
FIELD OF THE INVENTION
The present invention relates to an anode for chromium plating,
particularly an anode suitable for use in chromium-plating bath containing
additives of organic materials, and also relates to a process for
producing the anode.
BACKGROUND OF THE INVENTION
Conventionally, lead or lead-alloy electrodes have mainly been used as the
anode for chromium plating. Although the lead or lead-alloy electrodes
satisfactorily function to oxidize trivalent chromium ions formed on the
cathode to hexavalent chromic acid, its chemical and electrochemical
corrosion resistance is so poor that lead dissolves into the
chromium-plating bath to form insoluble lead chromate or lead sulfate,
which accumulates as sludge in the plating tank. In order to remove the
sludge, the plating operation is suspended.
As a substitute for the lead or lead-alloy electrode, an anode comprising a
substrate made of a valve metal such as titanium, and, formed on the
substrate, a covering layer containing a platinum group metal or an oxide
thereof, is coming to be used.
However, such an electrode obtained by covering a substrate made of
titanium or other valve metal with a layer containing a platinum group
metal or an oxide thereof has disadvantages as described below, although
use of this electrode as an anode for chromium plating is free from the
sludge formation accompanying the use of lead or lead-alloy electrodes.
Disadvantages include that the above electrode is costly, and, further
more, there is a problem that since the electrode is insufficient in
ability to anodize trivalent chromium ions resulting from reduction of
chromic acid on the cathode during plating into hexavalent chromic acid on
the anode, the concentration of trivalent chromium ions in the plating
bath increases, and, as a result, the plating bath weakens chromium
deposit-covering power. Also, there are cases where sufficiently glossy
deposits cannot be obtained. In addition, the electrical conductivity of
the plating bath decreases, making it difficult to conduct the chromium
plating normally.
Recently, chromium-plating baths containing various kinds of additives of
organic materials, such as sulfonic acid-based baths, have been developed
as substitutes for the conventional Sargent bath and hydrosilicofluoric
acid baths having considerable corrosive properties, and have come into
common use. Compared to the conventional Sargent bath, the
chromium-plating bath containing an additive of an organic material has
attained a higher cathode current efficiency and improved plating
efficiency, and also has an advantage that chromium-plated products
produced using this plating bath have improved quality.
Such a chromium-plating bath containing an additive of an organic material,
however, has a problem in that if a lead or lead-alloy electrode is used
as an anode in this plating bath, the electrode is consumed more rapidly
than the same electrode in the conventional Sargent bath; hence, such use
involves a problem.
A platinum-plated electrode obtained by covering a substrate made of a
valve metal such as titanium with platinum by electroplating is also being
used as an anode in plating baths, as an alternative to the lead or
lead-alloy electrode. Although this platinum-plated electrode has a high
electrode potential and is excellent in the ability to anodize trivalent
chromium ions formed by cathodic reduction into hexavalent chromic acid on
the anode, it is defective in that since the chromium-plating bath
contains an organic material, the platinum is consumed at a high rate,
and, hence, the thickness of the platinum deposit covering the substrate
should be increased in order to maintain long-term and stable chromium
plating. This raises the cost of the electrode. Therefore, the cost
advantage brought about by the replacement of the conventional Sargent
bath with the chromium-plating baths containing organic ingredients is
diminished.
On the other hand, as an expedient for improving the corrosion resistance
of an electrode obtained by covering a substrate made of a valve metal or
an alloy thereof with an electrode catalyst coating containing a platinum
group metal or an oxide thereof, provision of an intermediate layer made
of a composite oxide of stannic oxide and antimony oxide between the
electrode catalyst coating and the electrode substrate is disclosed, for
example, in JP-B-59-2753 and JP-B-61-36075 (the term "JP-B" as used herein
means an "examined Japanese patent publication"). However, any of such
intermediate layers is unable to be stably present in chromium-plating
baths and dissolves away within a short time period. For this reason, the
above intermediate layer is ineffective in preventing the deterioration of
the substrate and cannot retain its adhesion to the electrode catalyst
coating layer containing a platinum group metal or an oxide thereof and,
as a result, the voltage increases in a short period of time.
In addition, the electrodes having a catalyst coating comprising a platinum
group metal or an oxide thereof, for example, the electrode as described
in JP-B-59-2753 which has a ruthenium oxide coating, have been unable to
stand practical use because they show poor corrosion resistance when used
as an anode for plating, and, furthermore, their ability to oxidize
trivalent chromium ions into hexavalent chromic acid is poor.
JP-B-62-2038 discloses an electrode which comprises a substrate made of a
valve metal or an alloy thereof, having formed thereon an electrode
catalyst coating containing a mixture of a platinum group metal and tin
dioxide, and the consumption of which is reduced due to such a coating.
This electrode, however, is unsuitable for chromium plating because when
chromium plating is conducted using this electrode as the anode, oxygen
evolved during the electrolysis increases the voltage in a short time
period, making the electrode unusable any more.
SUMMARY OF THE INVENTION
The present inventors have conducted extensive studies to eliminate the
above-described problems. As a result, they have succeeded in developing
an anode for chromium plating which has the ability to sufficiently
oxidize trivalent chromium to hexavalent chromic acid, and which also has
good corrosion resistance.
That is, the present inventors have made studies with a view to reducing
the consumed amount of platinum for the platinum-plated electrode
excellent in the ability to anodize trivalent chromium ions into
hexavalent chromic acid and having a high oxygen-evolving potential, and
as a result, it has been found that the consumption of platinum in
chromium-plating baths containing additives of organic materials can be
reduced without impairing the properties originally possessed by the
platinum-plated electrode, by employing a platinum layer in which a
specific substance has been dispersed and by providing intermediate layers
having specific compositions.
An object of the present invention is to provide an anode for chromium
plating which is particularly suitable for use in plating baths containing
additives of organic materials.
Another object of the present invention is to provide a process for
producing the above anode.
Still another object of the present invention is to provide an electrolytic
chromium-plating method employing the above anode.
A still further object of the present invention is to provide an apparatus
for carrying out electrolytic chromium-plating, said apparatus using an
anode of the type described above.
The anode for chromium plating according to the present invention comprises
an electrically conductive substrate comprising a valve metal or an alloy
thereof, a first intermediate layer formed on the substrate and comprising
an oxide of tin, a second intermediate layer formed on the first
intermediate layer and comprising either (1) platinum metal and an oxide
of tin, or (2) platinum metal, an oxide of tin, and iridium oxide, and a
surface layer formed on the second intermediate layer and comprising
either (1) platinum metal and an oxide of tin, or (2) platinum metal, an
oxide of tin, and iridium oxide, the composition of the surface layer
being different from that of the second intermediate layer.
In another aspect, the present invention relates to a method for producing
an anode in accordance with the present invention as described above.
In still another embodiment of the present invention, there is provided a
method for electrolytic chromium plating which comprises conducting
electrolytic chromium plating using an anode of the present invention as
described above.
According to a still further embodiment of the present invention, an
apparatus for chromium plating is provided, comprising an anode which
comprises an electrically conductive substrate comprising a valve metal or
an alloy thereof, a first intermediate layer formed on the substrate and
comprising an oxide of tin, a second intermediate layer formed on the
first intermediate layer and comprising either (1) platinum metal and an
oxide of tin, or (2]platinum metal, an oxide of tin, and iridium oxide,
and a surface layer formed on the second intermediate layer and comprising
either (1) platinum metal and an oxide of tin, or (2) platinum metal, an
oxide of tin, and iridium oxide, the composition of said surface layer
being different from that of said second intermediate layer.
DETAILED DESCRIPTION OF THE INVENTION
The anode for chromium plating according to the present invention is
characterized as having an electrode catalyst coating comprising platinum
and an oxide of tin dispersed in the platinum. Although the electrode
catalyst coating contains an oxide of tin, the ability of platinum to
anodize trivalent chromium ions into hexavalent chromic acid can be fully
maintained because the tin oxide itself is low in electrochemical
catalytic activity, and hence has little influence on the platinum
electrode.
It is also possible, according to the present invention, to further
diminish the consumption of platinum by dispersing iridium oxide, along
with the tin oxide, into the platinum.
In producing the anode of the present invention, the electrode catalyst
coating comprising these components is formed on a substrate made of a
valve metal such as titanium, tantalum, niobium, zirconium, hafnium, or an
alloy thereof. However, since direct covering of the substrate with the
electrode catalyst coating results in insufficient electrode performance,
the coating is formed on the substrate not directly but through the medium
of intermediate layers. That is, before the electrode catalyst coating is
formed, a first intermediate layer comprising an oxide of tin is formed by
coating the substrate with a solution containing a tin compound and then
heat-treating the coating in an oxidizing atmosphere, and, furthermore, a
second intermediate layer containing an oxide of tin and platinum metal is
formed on the first intermediate layer.
The first intermediate layer serves mainly to improve the adhesion of an
electrode catalyst coating to the substrate and increase the electrical
conductivity between the coating and the substrate. Preferable effects can
be obtained when the amount of the tin oxide fixed on the electrode
substrate is from 0.5 g/m.sup.2 to 30 g/m.sup.2. A more preferred range of
the tin oxide amount is from 0.5 g/m.sup.2 to 10 g/m.sup.2. Amounts of the
tin oxide covering the substrate exceeding 30 g/m.sup.2 are not preferable
because such amounts lead to an increase in electrode potential.
On the first intermediate layer, a second intermediate layer comprising
platinum metal and an oxide of tin is formed by coating the first
intermediate layer with a solution containing a platinum compound and a
tin compound, and then heat-treating the coating in an oxidizing
atmosphere. This second intermediate layer may further contain iridium
oxide as the third component in addition to the two components, platinum
metal and tin oxide. Such a three-component covering layer can be formed
by coating a solution containing a platinum compound, a tin compound, and
an iridium compound, and then heat-treating the coating in an oxidizing
atmosphere.
In the case where the second intermediate layer is constituted by two
components, i.e., platinum metal and tin oxide, the proportion of the
former to the latter component is preferably from 30:70 to 60:40 by mol.
Part of the platinum contained in an amount in the above-specified range
may be replaced with iridium oxide in an amount so as to result in an
iridium oxido content of 10 mol % or less based on the total amount of the
platinum metal, tin oxide, and iridium oxide.
If the content of iridium oxide in the second intermediate layer exceeds 10
mol %, an oxygen-evolving reaction takes place on the second intermediate
layer because of the significantly high electrochemical activity of
iridium oxide as compared with platinum metal, and, as a result, the
electrode potential rises disadvantageously in a short period of time.
The second intermediate layer is exceedingly effective in improving the
adhesion of an electrode catalyst coating as a surface layer to the first
intermediate layer and the electrical conductivity between the two layers.
On the second intermediate layer, a surface layer which comprises platinum
metal and an oxide of tin and may further contain iridium oxide is formed
by coating the second intermediate layer with a solution which contains a
platinum compound and a tin compound and may further contain an iridium
compound and in which the relative amounts of the ingredients are
different from those for the second intermediate layer, and then
heat-treating the coating in an oxidizing atmosphere.
In the case where the surface layer is constituted by two components, i.e.,
platinum metal and tin oxide, the proportion of the former to the latter
component is preferably from 70:30 to 90:10 by mol. Part of the platinum
the relative amount of which to the tin oxide is in the above-specified
range may be replaced with iridium oxide in an amount so as to result in
an iridium oxide content of 10 mol % or less based on the total amount of
the platinum, tin oxide, and iridium oxide, thereby to form a
three-component surface covering layer.
If the platinum content in the surface layer is below 70 mol %, electrode
potential increases in a short period of time. If the platinum content is
above 90 mol %, the platinum is consumed at an increased rate. Further, if
iridium oxide is incorporated in an amount exceeding 10 mol %, the ability
of electrode to anodize trivalent chromium ions formed by cathodic
reduction into hexavalent chromium-based chromic acid is weakened because
iridium oxide has a low oxygen-evolving potential. For this reason,
iridium contents exceeding 10 mol % are not preferred.
In order to obtain the desired thickness for each covering layer of the
electrode, the coating and heat-treatment operations as described
hereinabove may be conducted repeatedly.
The anode for chromium plating according to the present invention, which
comprises an electrically conductive substrate comprising a valve metal or
an alloy thereof, a first intermediate layer formed on the substrate and
comprising an oxide of tin, a second intermediate layer formed on the
first intermediate layer and comprising either platinum metal and an oxide
of tin or platinum metal, an oxide of tin, and iridium oxide, and a
surface layer formed on the second intermediate layer and comprising
either platinum metal and an oxide of tin or platinum metal, an oxide of
tin, and iridium oxide, and in which the composition of the surface layer
is different from that of the second intermediate layer, shows exceedingly
good corrosion resistance, particularly when it is used in
chromium-plating baths containing additives of organic materials.
The present invention is explained in more detail by reference to the
following examples, which should not be construed as limiting the scope of
the invention.
EXAMPLE 1
Using stannic chloride, platinum chloride, and iridium chloride as raw
materials for electrode coating ingredients, various solutions for forming
first intermediate layers, second intermediate layers, and surface layers
were prepared by dissolving these compounds in hydrochloric acid.
The first intermediate layer-forming coating solution was coated by
brushing it on a titanium plate cleaned with hot oxalic acid, and the
coating was dried and then heat-treated at 550.degree. C. in an oxidizing
atmosphere. The above procedure of coating, drying, and heat treatment was
repeated to form a first intermediate layer having a desired thickness on
the titanium substrate.
Subsequently, a second intermediate layer and a surface layer were formed
on the first intermediate layer using a second intermediate layer-forming
solution and a surface layer-forming solution, respectively, in
substantially the same manner as that for the first intermediate layer.
Likewise, a total of eight kinds of electrodes were prepared in each of
which the first intermediate layer, second intermediate layer, and surface
layer had respective compositions as shown in Table 1.
TABLE 1
______________________________________
Fixed SnO.sub.2
Molar ratio of
amount in the
Pt:Sn:Ir in the
Molar ratio
first second Pt:Sn:Ir in
Electrode
intermediate
intermediate the surface
No. layer (g/m.sup.2)
layer layer
______________________________________
1 0.5 30:70:0 90:10:0
2 5 25:70:5 65:30:5
3 30 40:60:0 78:20:2
4 20 38:60:2 70:30:0
5 5 50:50:0 74:20:6
6 20 49:50:1 80:10:10
7 10 60:40:0 80:20:0
8 10 50:40:10 63:30:7
______________________________________
Using each of the thus-obtained electrodes of the present invention, which
were different in coating layer composition, as an anode, and using a
copper plate as a cathode, continuous electrolysis was conducted at
60.degree. C. in a chromium-plating bath containing 40 ml/l of organic
type additive MI-40 (manufactured by Canning Co., U. K.) at an anode
current density of 30 A/dm.sup.2.
The time period in which the anode potential rose by 1 V from its initial
value at the beginning of the electrolysis was measured for each anode and
taken as lifetime. As a result, the anodes were found to have lifetimes of
2,000 hours or more.
COMPARATIVE EXAMPLE 1
In the same manner as in Example 1, electrode Nos. 9 to were prepared which
were the same as those prepared in Example 1, except that they differed
from the electrodes of Example 1 in fixed tin oxide amount for the first
intermediate layer and in the composition of the second intermediate layer
and surface layer. The compositions of the first intermediate layer,
second intermediate layer, and surface layer are shown in Table 2.
TABLE 2
______________________________________
Fixed SnO.sub.2
Molar ratio of
amount in the
Pt:Sn:Ir in the
Molar ratio
first second Pt:Sn:Ir in
Electrode
intermediate
intermediate the surface
No. layer (g/m.sup.2)
layer layer
______________________________________
9 0 30:70:0 90:10:0
10 0.5 20:80:0 80:20:0
11 0.5 70:30:0 80:20:0
12 0.5 43:40:17 80:20:0
13 0.5 15:70:15 80:20:0
14 0.5 40:60:0 100:0:0
15 0.5 40:60:0 60:40:0
16 0.5 40:60:0 72:10:18
17 0.5 40:60:0 56:30:14
18 40 40:60:0 80:20:0
______________________________________
Using each of the thus-obtained electrodes as an anode for chromium
plating, electrolysis was conducted under the same conditions as in
Example 1. As a result, the lifetimes of electrode Nos. 9 to 14 were 1,000
hours or less, while those of electrode Nos. 15 to 18 were between 1,000
hours and 2,000
EXAMPLE 2
Electrode Nos. 19 to 26 were prepared under the same conditions as in
electrode Nos. 1 to 8 of Example 1. Using each of the thus-obtained
electrodes as an anode and using a copper plate as a cathode, 100-hour
continuous electrolysis was conducted in the same chromium-plating bath as
in Example 1 at an anode current density and cathode current density of 30
A/dm.sup.2. After completion of each electrolysis, the concentration of
trivalent chromium ions in the resulting chromium plating bath was
measured by redox titration. The results obtained are shown in Table 3,
from which it is seen that the trivalent chromium ion concentration for
each electrolysis was so low that the chromium plating was never impeded
by the chromium ions.
TABLE 3
______________________________________
Fixed SnO.sub.2
Molar ratio of
Molar Trivalent
amount in Pt:Sn:Ir in ratio of
chromium
Elec- the first the second Pt:Sn:Ir in
ion con-
trode intermediate
intermediate
the surface
centration
No. layer (g/m.sup.2)
layer layer (g/l)
______________________________________
19 0.5 30:70:0 90:10:0 2.9
20 5 25:70:5 65:30:5 3.2
21 30 40:60:0 78:20:2 3.0
22 20 38:60:2 70:30:0 3.5
23 5 50:50:0 74:20:6 3.6
24 20 49:50:1 80:10:10
3.3
25 10 60:40:0 80:20:0 3.3
26 10 50:40:10 63:30:7 3.7
______________________________________
COMPARATIVE EXAMPLE 2
Electrode Nos. 27 and 28 were prepared under the same conditions as in
electrodes of Example 1 except that the molar proportion Of iridium oxide
in the surface layer was increased. Electrolysis was conducted and the
concentration of trivalent chromium ions in the resulting plating bath was
then measured under the same conditions as in Example 2. The results
obtained are shown in Table 4, from which it is seen that the trivalent
chromium ion concentrations were unfavorably high for chromium plating.
TABLE 4
______________________________________
Fixed SnO.sub.2
Molar ratio of
Molar Trivalent
amount in Pt:Sn:Ir in ratio of
chromium
Elec- the first the second Pt:Sn:Ir in
ion con-
trode intermediate
intermediate
the surface
centration
No. layer (g/m.sup.2)
layer layer (g/l)
______________________________________
27 0.5 40:60:0 72:10:18
13.4
28 0.5 40:60:0 56:30:14
16.2
______________________________________
As described above, the anode for chromium plating according to the present
invention, which comprises an electrically conductive substrate comprising
a valve metal or an alloy thereof, a first intermediate layer formed on
the substrate and comprising an oxide of tin, a second intermediate layer
formed on the first intermediate layer and comprising either platinum
metal and an oxide of tin or platinum metal, an oxide of tin, and iridium
oxide, and a surface layer formed on the second intermediate layer and
comprising either platinum metal and an oxide of tin or platinum metal, an
oxide of tin, and iridium oxide, and in which the composition of the
surface layer is different from that of the second intermediate layer,
shows excellent durability when used in organic ingredient-containing
plating baths that are advantageous in providing chromium deposits having
excellent properties, so that the consumption of the anode can be
one-tenth to one-twentieth as large as that of conventional
platinum-plated electrodes and the anode enables chromium plating to be
conducted stably over a prolonged period of time.
While the invention has been described in detail and with reference to
specific embodiments thereof, it will be apparent to one skilled in the
art that various changes and modifications can be made therein without
departing from the spirit and scope thereof.
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